Close up of terraced agriculture on a steep mountainside in Dong Van, Vietnam. Photo Credit: Lori Shapiro

the open windows. Out those same windows, ancient rice terraces cultivated for thousands of years whizzed by, with the perfectly level cutouts making stairs climbing until the last bit of soil disappeared and the bare limestone mountain peaks began.

As the road began to wind through switchbacks on the way to the first pass, we began to discern more clearly what was outside our windows. We started to see large stands of cassava, planted into the steepest of slopes with no irrigation – marginal environments where many crop species often fail, but cassava can thrive. In many other places, the colors on the rice terraces were not the verdant green of closely packed rice plants that have been a ubiquitous staple for millenia, and is present in seemingly countless forms here in Northern Vietnam. Instead, we often saw co-culture mixes of bright red amaranth flower and seed heads, bright yellow pumpkin flowers calling for pollinators, and much taller corn stalks and cassava canopies; all crops of New World origin. This particular polyculture crop mixture would perhaps be much more appropriately placed in amilpaor home gardenon a mountainside in Mesoamerica.

How did these crops from the New World – cassava stands and milpa crop mixes – arrive in such high frequency in

A maize plot outside of a house in Vietnam. Photo Credit: Lori Shapiro

Sampling cassava on the side of a mountain. Photo Credit: Lori Shapiro

and harmful – of pumpkin, corn, and amaranth were left behind in the Americas. What has happened to the microbial mutualists we can’t see? Did they remain behind? Did they travel with the seeds to new places, hidden internally? Was cassava, which is transported by cuttings, able to carry its microbiome from the New World to Asia in a similar – or perhaps better – manner as plants that were introduced by seed, such as pumpkin?

To study how global crop plant movement affects ecologically important interactions, we stopped as the next cassava stand rolled into view, clinging

On our way to sample cassava on the side of a mountain with terraces and limestone peaks in the background. Photo Credit: Lori Shapiro

to the side of a steep incline, and our collaborator Thuy jumped out of the car. She carefully sterilized her plant surgical tools – scissors for cutting leaves and roots, and a metal spoon for digging bulk soil away from plant roots. She sampled leaves, flowers, stems, and roots into labeled sterile bags, quickly sealed the bag, and moved on to sample the next plant. We repeated this process with cassava, maize, pumpkin, cucumber, and luffa.

Now that we have returned to the lab, we are extracting DNA from these samples to contribute to the

We anticipate that this project – building libraries of the world’s crop plant associated microbes; understanding their structure, function, and geographic variation; and how human activities may have interrupted plant-microbe relationships – will continue for many years in the future. Stay tuned as we add more crop plants, and more places to our sampling.